The conventional inversion type MOS-FET triode has several characteristics which limit its high frequency response. These include:
(a) The existence of a gate to drain overlap capacitance.
(b) The mobility of the carriers in the inversion layer is limited by surface scattering effects to roughly the half of its bulk value.
(c) Conventional photolithographic techniques restrict practical channel lengths to the order of 5.mu.m or longer.
Drawbacks (a) and (b) can be remedied by using a built-in channel with an offset gate structure, that is, a gate structure which is not located in the center of the triode. Such a device is provided by first growing an epitaxial layer of semiconductor material upon an insulating substrate. If the epitaxial layer is an n-type semiconductor material, n.sup.+ -type semiconductor source and drain regions are formed by techniques such as a solid-state diffusion, so that an n-type semiconductor channel is disposed between two n.sup.+ -type semiconductor regions. The gate area is only partially metallized in order to avoid overlapping with the drain region. In this way the gate-to-drain overlap capacitance is minimized. The above described device functions as an ordinary built-in channel MOS-FET device. The minimum length L', of the n-type semiconductor channel is determined essentially by the photolithographic process and will be of the order of 5 .mu.m. In conclusion the conventional offset gate built-in channel MOS-FET does not have drawbacks (a) and (b). However, the effective channel length is still long (5 .mu.m) and limits the operation of a built-in channel MOS-FET at high frequencies.